You want the clear steps, but within one step you want a mix of maybe 50:50 with the next texture?
Do you want a complete, even mix and no steps / stripes?
You can try the Smoothstep knot instead of the step to see if it gives you something to ask for. However, you need a range of values for your masking textures, not just different 3 values
You may need Remaps + Lerps to do certain things based on your question
or you can paint the full masking mix into each R, G, B channel
and let R only mix with G and G only mix with B (depends on whether you only need 2 mixes against 3)